Completely brand new to DSLR, so picked up a second hand E600 from CEX.

I've noticed that when shooting with the viewfinder, the final image isn't where I aimed, and comes up slightly higher than I wanted. I can compensate by aiming slightly lower, but I really want it to just centre with the cross hairs.

One thought - does the E-600 have an interchangeable focusing screen? I think the E-1 did, not sure about others. If it does, it could have been put back in slightly misaligned which could give rise to the problem.

From what I can see, the focusing screen is interchangeable, but the fit of it is quite tight it's hard to see that it could be misaligned...

I changed the focusing screen on my E-500 and if I remember correctly, it fits very precisely in one orientation only. Assuming there's nothing obstructing the mirror from returning to it's correct position, could it be the mechanism has got lazy and with lots of use, will correct itself.

So it's definitely a viewfinder fault. I suspect it will be the focusing screen or the penta prism or mirror(not sure what the E600 has).
If it was the mirror misaligned I think you'd see a line along the top or bottom.